This story went around a bit last week. I didn't pay it much mind because it originated on BatmanOnFilm, which has basically zero substantial credibility on news items, but now it's getting some attention from more reputable sources, so it deserves at least a look.
Anyway. BoF's gossip is that Wonder Woman's actual role in "MAN OF STEEL 2: SORRY ABOUT MAN OF STEEL 1 BUT HEY LOOK WE'RE GONNA DO JUSTICE LEAGUE WE PROMISE" will be more of an extended cameo akin to Black Widow in "IRON MAN 2." That actually sounds plausible, and goes with what I've been hearing all along - that the original plan was for other Leaguers to turn up as wink-wink bit-players in their civilian identities, with "Oh, shit! That was actually Wonder Woman/Flash/Lantern/Whoever!" as a stinger or a post-credits sequel tease, but that WW and maybe others were being expanded to full onscreen cameos by producers who are anxious for anything that will help market this as something closer to the popular "AVENGERS" than the profitable-but-divisive "MAN OF STEEL" (real-talk: like it or not, the writing is on the wall: 2013 ended with MOS as a punchline/whipping-boy for gloomy, bloated, poorly-scripted genre movies - it's this year's "PROMETHEUS.")
The next part of the "rumor," though, doesn't thus far seem to have any substance backing it up beyond "Yeah, I can believe this production team would screw up in this specific way." According to BoF, the plan is to sidestep having to explain Wonder Woman's more whimsical/mystical background... by making her another Kryptonian.
Yup, that sounds entirely believable. Maybe (hopefully!) not true, but 100% in-line with the reductive small-universe "streamlining" that too many people still think is needed/preferred for these movies.
The "full" pitch is that The Amazons are actually descendants of survivors from that crashed/abandoned Kryptonian outpost Superman found in "MAN OF STEEL," with Krypton's genetic-engineering angle explaining how they managed to create an ongoing all-female society. I imagine that there'd probably be some throwaway lines about wandering-Kryptonians being the basis of the Greek Pantheon (among others) itself dropped in as well. Magic? Mythology? NO! That's too much, you can't start doing magical stuff when it started as a scifi-franchise! "Too many audience buy-ins," to use studio idiot-speak.
Setting aside the fact that this would rob the character of everything that makes her unique and interesting, reducing her to just Supergirl with a different name, it's so bloody pointless. The main, all-important advantage that the "big three" JLA heroes have over everything else in the genre is that everyone already knows them. Maybe not the specifics, maybe not the whole history, but if Wonder Woman shows up midway through this movie and starts throttling bad guys NOBODY who was going to see this in the first place is going to be taken out of the movie in bewilderment: Everyone has heard of Wonder Woman, everyone knows throttling bad guys is what superheroes "just DO," you can even get a laugh (remember those?) by setting the origin-story aside for later with a line or two:
"And you are...?" "Wonder Woman." (or "Diana," if we're still doing the "heroes embarassed by their nicknames" bullshit) "Where did you...?" "It's complicated. Shouldn't you be punching Luthor/Doomsday/Parasite/whoever?" Ha ha. Audience giggles, action resumes, toss in a couple "Great Hera's!" to nudge the fans, end on a "We should totally start a club, you guys!" and figure out how to explain "Magical Island of Immortal Hellenistic Lesbians" in the next one (or in WW's solo featu... oh, right. "Girl movies don't make money." I forgot.)
Now I wonder if this has been part of the plan all along, hence the constant go-nowhere reminders of Krypton's abandoned space program in the first movie: A handy way to explain any number of brand-name metahumans without having to get into the various magical/alien/interdimensional backgrounds that inform the DC multiverse. Hawkman/Hawkgirl? Kryptonians plus wings. Aquaman (and maybe all the Atlanteans)? Water Kryptonians. Darkseid? The New Gods? Ditto.
All conjecture, of course, but like I said... it's all so depressingly possible.